This is the best advice. Always email HR before the interview. This will give you much more comfort going into the interview. We all know that the anxiety levels are much higher when speaking to a new person who is not aware of the stutter. In one of my first interviews in college, I did not tell the employer beforehand of my stutter. About 10 minutes into the interview, which I had thought was going well, they asked me "are you okay?" as I was stammering through a question. This destroyed my confidence, but, I actually ended up getting the internship. Another option is to get a Schedule A designation letter for the stutter. I did this the next year in college to help me get government internships.